"Now, [the test plot] is just one ecosystem, and you can't make global claims from one alpine meadow," Harte cautioned. "But bogs, prairie, and tundra ecosystem studies are beginning to show similar results."

Vanishing Ice

Elsewhere real-life signs of global climate change blanket the globe.

When Montana's Glacier National Park was established in 1910, it held some 150 glaciers. But now fewer than 30 glaciers remain and they are greatly reduced.

In Tanzania the legendary snows of Mount Kilimanjaro have melted by some 80 percent since 1912 and could be gone by 2020.

"We know that most of the world's small glaciers are shrinking," said Mark Serreze of the National Snow and Ice Data Center at the University of Colorado at Boulder.

"A few are still advancing. But if you want to see Kilimanjaro or go to Glacier National Park to see glaciers, you'd better go soon. Because they're on their way out."

Arctic regions are feeling even more heat and will be among the most altered over the next few decades.

Temperatures there have already increased as much as 4° to 7°F (3° to 4°C) in the past 50 yearsnearly twice the global average.

They're projected to rise 7° to 13°F (4° to 7°C) over the next hundred years, according to the Arctic Climate Impact Assessment, a multinational study.

Some Arctic coastal communities are already pondering relocation. Thawing permafrost poses an infrastructure disaster, as homes, roads, and pipelines that were built on once-frozen ground begin to shift or sink.

"The one surprise for me is how rapidly [warming] is happening, how sensitive ecological resources are to climate change," said ecologist Hector Galbraith, of Galbraith Environmental Sciences and the University of Colorado at Boulder.

Galbraith expects that over the next two decades, the Earth will see an acceleration of ecosystem changes already under way. Such alterations will include different migration and breeding seasons for some animals and new flowering seasons for plants.

"But mobile organisms, like birds, can simply move. We're already seeing major range extensions of species like Acadian flycatchers and red-bellied woodpeckers."

Such adaptations could mean major and unpredictable ecosystem changes.

"A lot of the northern forests are very susceptible to insect attacks, and songbirds are a major [source of] control," Galbraith continued.

"If the birds move north, forests may be more susceptible to insect attacks, which means more dead wood, which means more fire. The whole nature of the forest can change fairly quickly."

Fires can also be outgrowths of droughts and severe weather, which many scientists expect to increase as the Earth warms.

One such scientist is Sir John Houghton, former chairman of the Intergovernmental Panel on Climate Change's scientific assessment.

In testimony last week to the United States Senate's Energy and Natural Resources Committee, Houghton referenced the unusually extreme heat wave that killed some 20,000 central Europeans during the summer of 2003.

"Careful analysis shows that it is very likely that a large part of the cause of this event is due to increases in greenhouse gases and projects that such summers are likely to be the norm by the middle of the 21st century and cool by the year 2100," Houghton told the committee.

Busalacchi, the University of Maryland meteorologist, cautions that it is difficult to attribute any single extreme weather event to global warming. "But that episode is a very good example of what we expect to see more of in the future," he said. (See "Global Warming Unstoppable for 100 Years, Study Says.")

Like severe weather, many of global warming's near-term effects will be felt regionally, resulting in relative "winners" and "losers."

"There's likely to be a very large disparity of impact between the developed and developing world," said Anthony Janetos, director of the Heinz Center for Science, Economics, and the Environment's global change program.

"We know that there's a large disparity in the capacity to deal with that impact, which creates some challenges for the policy community."